This invention relates to replaceable cylinder liners for internal combustion engines, including very efficient diesel engines with high brake mean effective pressures. However, certain applications for the present invention may be outside of this field.
Replaceable cylinder liners provide significant advantages to internal combustion engines, especially those engines intended to have extremely long periods of time between overhauls. Engines such as truck diesel engines may be designed for two million hours of usage between overhauls. At the time of overhaul, the cylinder liners of such engines can be removed and replaced and the engine block reused with another set of liners. Further, at the time of manufacturing, replaceable liners eliminate the need for precision finishing of long bores in a block, shifting that process to a smaller, more economical operation on an individual liner.
The continuing need for more thermally efficient engines has placed additional demands on the cylinder liner. Increased thermal efficiency can be achieved by increasing the brake mean effective pressure (BMEP) of the engine. Advanced diesel engines are capable of BMEP in excess of 300 psi. These very efficient engines have very high combustion temperatures. A portion of the combustion energy not converted into work or expelled as exhaust gas must be dissipated, and a portion of this energy is dissipated as heat conducted through the walls of the cylinder liner and into the cooling system. If this heat is not properly removed from the cylinder liner, there can be numerous problems. One such problem involves overheating of the top piston ring.
Unlike the bottom piston ring and the piston itself, the top piston ring receives only limited cooling from the engine oil supply. Unlike the bottom ring, the top piston ring is directly exposed to combustion gases. If the top piston ring overheats, oil in contact with the ring from the cylinder wall inner diameter will be converted to coke, with an accompanying loss of lubrication. Ring and liner wear will be accelerated as a result, and ring failure made more likely.
One method of removing heat from the top piston ring involves improved cooling of the cylinder liner. A cooler cylinder liner will conduct more heat away from the top piston ring. Various ideas have been proposed for improved cooling of replaceable cylinder liners. These ideas, as well as ideas generally relating to cylinder liners, can be found in the following U.S. Patents:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 4,244,330 Baugh et al. 1/13/81 4,305,348 Martin 12/15/81 4,616,603 Kubis et al. 10/14/86 4,638,769 Ballheimer 1/27/87 4,867,118 Kubis et al. 9/19/89 5,048,468 Broughton et al. 9/17/91 5,150,668 Bock 9/29/92 5,299,538 Kennedy 4/5/94 5,343,837 Ward et al. 9/6/94 5,575,251 Bock 11/19/96 ______________________________________
There is a continuing need for improved cooling of cylinder liners. The present invention provides a novel and unobvious apparatus and method for improved cooling of cylinder liners.